Clear pressure-sensitive labels, in particular beer labels, are very often comprised of the following construction: A release liner of PET film is coated on one side with a release agent, commonly a silicone polymer, which is coated with a pressure-sensitive adhesive. This pressure-sensitive adhesive is dried at elevated temperature and after that a facestock is laminated onto the adhesive side. The adhesive then, under the pressure of the lamination process, transfers to the film facestock. The film facestock is typically a clear polypropylene film with a thickness typically between 20 and 60 microns.
This self-adhesive construction is then slit to the required narrow width suitable for further conversion by a pressure-sensitive label printer. The next step in the label production process is that the label printer prints a plain non-pressure-sensitive clear film, typically a BOPP or PET film, on the reverse side and then laminates this reverse-printed film with a suitable laminating adhesive to the pressure-sensitive construction supplied by the label-stock producer. This overlaminate typically has a thickness of between 12 and 40 microns.
This film is printed on the reverse side in order to provide scuff resistance to inks in addition to the fact that brilliant silver and gold metallic colours demanded by brand-owners, in this case breweries, can only be achieved when solvent-based silver inks are gravure-printed on the reverse side of a clear film which, when viewed from above, gives the high brilliance required due to the metallic pigments shining through the clear film.
The laminating adhesive used is most commonly a polyurethane adhesive, often solvent-based, which represents an environmental hazard as well as a fire and explosion risk. This whole process through the chain is complex, cumbersome and costly.
Publication U.S. Pat. No. 6,540,865 discloses a release liner which is coated with a release agent and subsequently coated with an adhesive, on top of which a second detackified layer (DL) is applied to the surface of the pressure sensitive adhesive forming a continuous film covering the PSA layer. This non-tacky layer allows the construction to be rolled-up and stored. It can then be later activated by heat for subsequent lamination to another substrate.
This detackified layer having typically a grammage of 10-15 g/m2 and containing the preferred heat-sealable polyamide resin is very expensive, adding considerable cost and complexity to the overall construction.
In a commercial printing process operating at normal process speed, the activation of such a detackified layer and subsequent lamination to a clear plastic film will not yield a perfectly clear, water-white and imperfection-free film demanded by the beverage industry for clear labels.
Publication WO 99/49440 discloses a pressure-sensitive construction in which a pressure-sensitive adhesive is applied to a release-coated surface of a liner, and on top of the pressure-sensitive adhesive, a non- blocking non-preformed film material is applied which covers the pressure-sensitive layer, rendering it tack-free. Suitable film-forming materials include thermoplastic polymers, such as polyolefins, polyvinyl chloride, polyesters, or polyamides which could be extrusion coated or applied in a liquid or molten state to the top surface of the pressure-sensitive adhesive.
This construction comprising liner, pressure-sensitive adhesive and continuous film layer is claimed to be printable, die-cuttable, matrix-strippable, and dispensible, thereby eliminating the use of conventional facestock materials. Furthermore, it can be overlaminated with plain or preprinted clear overlaminating films. However, this is an extremely complex and costly manufacturing process.